A switchgear unit is generally also referred to as a load feeder and is usually arranged in a switchgear cabinet on a standardized top-hat rail next to other load feeders. The load feeders arranged in a switchgear cabinet are assembled in a modular fashion in order to make it possible to meet the respective requirements. Load feeders of this type are provided in particular in industrial systems for controlling and switching high currents and voltages. The switchgear unit is used in particular to drive a three-phase motor. The switchgear unit is in this case also referred to as a motor starter.
The switchgear unit of a motor starter generally has three functions for protecting the motor. The first function is that of switching the motor during operation, and is performed by a dedicated standard unit, usually a so-called contactor. The contactor is designed to repeatedly switch high currents on and off, during operation. Furthermore, in a switchgear unit, the functions of short circuit protection and overload protection are integrated in a standard unit referred to as a power breaker. The power breaker isolates the load from the power supply system when a short circuit occurs and also when the current is too high. The two standard units are arranged next to one another on a common carrier and form the switchgear unit.
DE 43 35 965 discloses a motor starter having integrated short circuit protection and in which a power breaker, an electronic tripping unit and a contactor are arranged one behind the other. The electronic tripping unit is integrated together with the power breaker in a common enclosure. The tripping unit in this case has a release which provides the thermal overload protection for the motor.
FR 2 003 575 discloses a contactor having a short circuit release which is provided as an attachment and having an attachment which contains a thermal overcurrent release.
WO 99/23737 discloses a switchgear unit which has a contactor and a power breaker, each as separate units. These units are arranged on a subcarrier in which a printed circuit board with electronics is integrated. Such electronics make it possible to drive the switchgear unit by way of a bus system. In this case, in particular two bus systems are provided, that is a data bus for interchanging signals and a power bus for supplying power. As an alternative to the standard units of the contactor and the power breaker, an electronic circuit is proposed which is, however, less suitable for switching very high currents than the electromechanical units of the contactor and the power breaker, or is very complex and expensive.